1. Field of the Invention
This invention relates to an image reader.
2. Description of the Related Art
Hitherto, an image reader configured to read an image from an original by a linear image sensor including three image reading elements corresponding to R (red), G (green), and B (blue) has been known. This kind of image reader can read a color image from an original using the three image reading elements and can also read a monochrome image from an original using one image reading element (for example, corresponding to G (green)).
In recent years, an image reader configured to read an image from an original by a linear image sensor further includes one image reading element, which serves as an image reading element dedicated to reading of a monochrome image in addition to the three image reading elements has been known. (JP-A-2002-111968) This kind of image reader can read a color image from an original using the three image reading elements dedicated to reading of a color image and can also read a monochrome image from an original using one image reading element dedicated to reading of a monochrome image.
However, the image readers in the related arts involve the following problems:
In the image reader, a flatbed mechanism (FB) or an automatic document feeder (ADF) is used to read an image from an original. That is, either one of the image sensor and an original is moved relative to the other by the FB or the ADF for the image sensor to scan over the original in the range of a read start position to a read end position.
However, the three image reading elements used to read a color image and the one image reading element used to read a monochrome image (=one of the three image reading elements used to read a color image or one image reading element dedicated to reading of a monochrome image different from the three image reading elements used to read a color image) differ slightly in a read target position.
Thus, if the positional relationship between the image sensor and the original at the start time of a relative move, the timing of starting the relative move, which will be hereinafter referred to as the move start timing, and the timing of actually starting read processing of the original by the image sensor, which will be hereinafter referred to as the read start timing, for reading a color image are all matched with those for reading a monochrome image, the scan ranges over the original do not strictly match. As a result, the image in the same range cannot precisely be read; this is a problem.
As for the problem, if the read start timing is a little delayed for either one of the case where a color image is read and the case where a monochrome image is read, it might be possible to match the scan range over the original with that for the other.
In this case, however, the read start timing is a little delayed rather than the move start timing and thus the read termination timing is also delayed; there is a problem of somewhat increasing the time required from the move start timing to the read termination timing.